If there had been a goalkeeper in his goal, he wouldn't have taken the shot. Insane argument. It was all about opportunism timing, audacity, speed of thought, skill and flawless technique.
He had a split second to react to the surroundings and intentionally hit it where and how he did BECAUSE there was no keeper. He was celebrating before it went in, because it was deliberate. And to be clear, these situations occur in matches up and down the country on a regular basis... Keeper comes rushing out, clears it, lands to a player in the opposition half... And 999 times out of 1000, the player it falls to will take a touch before he shoots, if he shoots at all. Most people would control it and lay off to a winger to start a counter.
Simple logic tells you its easier to hit a ball further when it's bouncing in step with you and you can get under it, than it is to hit a ball bouncing towards you, and from further away as well.
And further to the argument, Sigurdsson's goal, the keeper was on the edge of the box when it fell to him, and it didn't go in the top corner like some are saying either. It dropped just over the line if I remember correctly.